Automotive Braking Question

I have a 2008 Mustang GT. Decently sized disc brakes, not the best, but adequate for the performance level of the car.

Anyhow, its been my observational experience that front brakes work much harder than the rear brakes (which is why front rotors/calipers are often much larger than the rear brakes, as is the case on my car) due to weight transfer when braking, the weight of the engine being in the front (in most cars), etc.

This also manifests itself in the accumulation of brake dust. I am in the car wash business and I see so many front wheels that are filthy while the rear wheels are practically brake-dust free. BMW’s and Volvo’s seem particularly notorious for mass amounts of brake dust generation (why is that anyway?) on the front wheels.

Which leads to my question. I have been noticing that when I clean my car, which is often, wiping down the rear wheels results in more brake dust than the fronts.

Last time I got my car serviced, in which they do a multi-point inspection, they listed the rear brakes as having 7 (out of 12) millimeters of life while the fronts had 8mm.

Why is this? Why would my rear brakes, being smaller and in the lighter rear end of the car be wearing faster than the fronts?

Do you have a lot of junk in the trunk, perhaps?

Maybe you have ceramic pads on the front?
Have you had the brakes serviced? I’m not that familiar with the 2008 GT, but that was a performance model, wasn’t it? Perhaps it came from the factory with ceramic pads?

When I re-did the brakes on my car, I replaced the front pads with ceramic ones and I am very happy with the lack of brake dust.

excavating (for a mind)

Faster rear brake wear is an issue on a lot of newer cars. What’s going on is that the brake bias is more towards the front during heavy braking, but is closer to 50-50 during routine soft braking. Since the back brakes have to do less work during heavy braking, the car makers can use lighter-duty components which wear out faster during routine use than the heavier duty parts on the front.

So the solution is you need to take the car out to the track and do more hard braking in order to even things out.

I agree that different compounds are the most likely candidate. I wouldn’t be so sure that the rear is lighter than the front either. Something like a Mustang would have a lot of development toward a 50/50 weight bias, and the modern V8 is surprisingly light. A modern LS1 Corvette engine weighs less than the four cylinder in a 1980s Ford Escort. It’s possible that there’s a slight rear weight bias. Of course, wherever the weight lies, the center of gravity shifts forward when you brake.

That makes sense, especially since the rear brakes are smaller in every regard than the fronts.

This makes no sense to me and cannot possibly be true. There’s no way a V8 LS1 engine weighs less than a 4 cylinder in an Escort. I don’t think Ford even makes the Escort anymore.

By the way, this solution is hilarious, if likely true. LOL. I am not a track driver…just a normal dude…

The culprit (if you can call it that) is a feature in the braking system called EBD (electronic brakeforce distribution) or perhaps another name by other car makers.
Basically the system biases the rear brakes to generate a couple of percent more wheel slip during light to moderate brake application. This allows the system to automatically adjust for the amount of junk in the trunk. This has the effect helping make the front brakes last longer.

If you’re interested in becoming a track driver, see here.

They certainly don’t make the 80’s Escorts anymore.

Does this possibly have anything to do with the traction control? I mean, its a rear wheel drive car. The TC engages (AFAICT) under heavy acceleration to reduce wheelspin, engaging the rear brakes in order to do that. Could it possibly be engaging under less than wheelspin producing conditions?

FTR, there is literally nothing in the trunk and the rear end of the vehicle is pretty light.

Why would you engage the rear brakes under a no wheel spin acceleration condition? The only reason I could think of would be because the gas mileage numbers are too good and you are trying to fix them. :slight_smile:
The theory behind traction control is simple. No matter how much power the engine makes it is useless if you can’t put it to the ground.
TC systems use various methods to reduce wheel spin, retard timing, close the throttle, shut off individual injectors momentarily, and engage the brakes on the drive wheels.
On the systems I am familiar with that use the brakes it works like this: one drive wheel starts to spin, ABS pump energizes and applies the brake to the slipping wheel, wheel regains traction then either the other wheel looses traction or the same wheel looses it again. Again the brakes is applied to the slipping wheel. Lather rinse repeat until the car is above 25 mph or full traction is regained.
One limitation in this system is that if you floor it the system disengages.
As far as stuff in the trunk goes the designers of the brake system had no clue if your trunk is going to be empty or full of lead on any given day so they designed a system to adapt for the load in the trunk.

Ah, that makes sense Rick. Thanks.

On another note, I find it highly impressive that the new 2013 Shelby GT 500 doesn’t get dinged with the gas guzzler tax, despite making 662 HP and 620-plus ft/lb of torque. And where else on the planet can you get that kind of performance for 60k?